fix: return python interpreter exit status from pynvim-python #599

Problem: python interpreter exit status is ignored by pynvim-python.

For example:

```console
$ pynvim-python -c 'import sys; sys.exit(5)'; echo $?
0
```

Solution: propagate the exit status from pynvim-python.

Use `sys.exit()` to return the interpreter's exit status as found in `subprocess.run().returncode`:

```console
$ pynvim-python -c 'import sys; sys.exit(5)'; echo $?
5
```

Author: drmikehenry

pynvim/python.py

@@ -25,4 +25,4 @@
 
 def main() -> None:
     """Chain to Python interpreter, passing all command-line args."""
-    subprocess.run([sys.executable] + sys.argv[1:])
+    sys.exit(subprocess.run([sys.executable] + sys.argv[1:]).returncode)